Exemplification of AC2’s multidimensional capabilities to the application of large pools within the frame of the German EASY project

Abstract

Realistic numerical predictions of dynamic, complex, multidimensional flow scenarios occurring in light water reactors are vital prerequisites for every reliable safety assessment study. System analysis codes employing only one-dimensional fluid-mechanics models may fail to realistically capture the complex flow conditions in large scale passive components of light water reactors.Even though today’s CFD codes are capable of accurately representing multidimensional flow behaviour, they require huge computational efforts to simulate long-term transients. The German thermal-hydraulic system code (THS) ATHLET (Analysis of Thermal-hydraulics of LEaks and Transients) part of the AC2 simulation environment, is being developed by GRS (Gesellschaft für Anlagen- und Reaktorsicherheit gGmbH) for the analysis of the whole spectrum of operational transients, design-basis accidents and beyond design-basis accidents anticipated for nuclear energy facilities. The code provides a wide range of specific models for several light water reactor designs of Generation II, III+ and IV. Currently, the code’s one-dimensional six-equation two-fluid model, is being extended towards a fully three-dimensional set of thermal-hydraulic conservation equations. Until now ATHLET’s ability to capture multidimensional flow behaviour has mainly been assessed for the flow mixing behaviour in the reactor pressure vessel. Within this work, ATHLET’s capabilities to capture the multidimensional flow behaviour will be assessed for the flow within large scale passive components of light water reactors.These analyses highlight the advantages of ATHLET’s newly developed 3D model for the simulation of large scale passive systems.